1. Field of the Invention
The present invention relates to a polyamide composition and a molded article therefrom. The polyamide compositions of the present invention have excellent moldability, toughness, light-weightness, as well as excellent hot water and steam resistance, heat resistance, mechanical characteristics, low water absorption and chemical resistance. The polyamide compositions of the present invention can be used as molding materials for industrial materials or household goods.
2. Description of the Background
Crystalline polyamides represented by nylon 6 and nylon 66 have been used widely in fibers for clothing or industrial materials, and as general-purpose engineering plastics, because they have excellent properties and melt moldability. Such general-purpose polyamides are, however, pointed out to have problems such as insufficient heat resistance and poor dimensional stability due to water absorption. Particularly in recent years, polyamides to be used in the fields of electrical and electronic parts, automobile parts and engineering plastics have been requested to have high-level of properties. For example, with the development of the surface mounting technique (SMT) in the fields of electrical and electronic parts, polyamides are required to have high heat resistance such as solder resistance. Also in the fields of automobile parts including engine room parts, polyamides having more improved heat resistance than the conventional ones are demanded. As they have come to be used for a variety of applications, polyamides superior in physical properties and functions are requested not only in the field of electrical and electronic parts and automobile parts but also in the other fields. There is a strong demand for the development of polyamides excellent in dimensional stability, mechanical properties and chemical resistance as well as high heat resistance.
To meet the above requirements, semiaromatic polyamides comprising terephthalic acid and 1,6-hexanediamine as main components (hereinafter referred to as 6-T polyamides) are proposed. Aromatic polyamides comprising terephthalic acid and 1,6-hexanediamine have a melting point near 370° C., which exceeds the decomposition temperature of the polymer and hence cannot be melt molded. The 6-T polyamides are therefore currently used after modification to decrease their melting point to about 280-320° C. by copolymerizing 30 to 40 mole % of a dicarboxylic acid component such as adipic acid and isophthalic acid or a lactam such as ε-caprolactam and laurolactam. However, copolymerization of such a large amount of a third component and, in some cases, further a fourth component, which is effective in decreasing the melting point of the polyamide, also decreases the rate of crystallization, the attainable degree of crystallization, heat resistance and thermal stability, thereby reducing the obtainable properties such as rigidity at high temperature, chemical resistance and imensional stability, melt stability and prolonging the molding cycle to decrease productivity.
U.S. Pat. No. 5,670,608 discloses a polyamide (which will hereinafter be abbreviated as “PA9-T”) comprising (i) terephthalic acid and 1,9-nonanediamine or (ii) terephthalic acid, 1,9-nonanediamine and 2-methyl-1,8-octanediamine. PA9-T does not involve a problem upon practical use because it has a melting point at about 320° C., and it exhibits excellent properties in rigidity at high temperature, chemical resistance, dimensional stability and melt stability. When the polyamide is molded using a steam-heating or hot-water-heating type mold, however, insufficient crystallinity of the polyamide at low mold temperature makes the molded articles have reduced properties such as rigidity at high temperature and dimensional stability. In practice, therefore, PA9-T needs a mold temperature, upon injection molding, as high as 140° C.
Japanese Patent Laid-Open No. 2000-86759 discloses a polyamide comprising terephthalic acid, 1,9-nonanediamine, 2-methyl-1,8-octanediamine and an aliphatic dicarboxylic acid such as adipic acid and sebacic acid. The polyamide has sufficient crystallinity even by molding with a steam-heating or a hot-water-heating type mold, and also has excellent properties in rigidity at high temperature, dimensional stability, toughness, chemical resistance and melt stability. It is, however, recognized that the copolymerization of an aliphatic dicarboxylic acid leads to reduction of heat resistance of the polyamide.
In the fields of electrical and electronic fields, the surface mounting technique (SMT) which needs high heat resistance has came to be popular. The polyamide, described in Japanese Patent Laid-Open No. 2000-86759, prepared by copolymerization of an aliphatic dicarboxylic acid, however, cannot meet such a requirement.
There is, therefore, a demand for a polyamide having sufficient crystallinity even by molding with a steam-heating or a hot-water-heating type mold without a reduction of heat resistance of PA9-T.